For reasons of safety and/or information technology, present-day battery systems, for example traction batteries in the automotive sector, are equipped with a battery management system. A battery management system (BMS) of this kind obtains measured data of individual cells as well as measured variables for the overall battery, and is capable of identifying therefrom, inter alia, an instantaneous battery charge state as well as prognoses of the performance of a battery with regard to charging and discharging, in particular for time periods requested by a main vehicle control device. Calculation algorithms that detect the aging of individual battery cells and ascertain instantaneous battery parameters for the aforementioned algorithms are also utilized.
A first data input to or parameter determination for the charge state algorithms and power prediction algorithms is accomplished on the basis of highly accurate measured data for the current and voltage of individual cells or of the entire battery, from test-stand measurements on the individual battery cells. After installation in a vehicle, however, the cells are subject to time-related aging. This in turn must be detected online in the vehicle so that reparameterization based on cell aging can be carried out.
To allow high-quality reparameterization to be carried out, fast sampling operations for the individual cell voltages and for the current occurring in that context are carried out. A sampling operation is preferably accomplished with a time window <50 ms, for example at a 1-ms interval, in order to exactly detect a voltage dip due to ohmic resistance. For a preferred reparameterization, a synchronous sampling of the individual cell voltages and of the pertinent current can be selected.
FIG. 1 shows an exemplifying embodiment of a hardware architecture of a conventional battery management system.
FIG. 1 has a plurality of individual cells 4 that are connected in known fashion to a cell supervision circuit (CSC) element 6. The individual CSC elements 6 are connected via a data bus 8a to one another and to battery control unit (BCU) element 7. BCU element 7 can have a variety of sensors, for example current measuring sensors, connected to it, and can apply control via relay drivers to relays of battery system 2. The battery management system is connected to further control devices in the vehicle, for example, using a vehicle-internal communication bus 8b, for example a CAN bus.
The measurement of individual voltages of individual cells 4 is handled by the respective CSC element 6 that is connected to the individual cell or cells 4. CSC elements 6 are connected via data bus 8a to the main battery management control system device, i.e. BCU element 7.
FIG. 2 shows an exemplifying embodiment of a CSC element.
An individual voltage measurement of an individual cell 4 is accomplished as a rule via a special component of CSC element 6 which senses the voltages of individual cells 4, as a rule six or twelve individual cells 4; converts these measured values from analog to digital using one or more A/D converters in the individual voltage measurement chip; and sends these ascertained measured values, using bus system 8a, to the main battery management system circuit board, BCU element 7. A CSC element 6 of this kind can furthermore also have a plurality of temperature measurement points.
A so-called “companion chip,” which can carry out limit value monitoring with regard to the cell voltages, is usually also provided in CSC element 6 for safety reasons. A cell balancing element can also be provided in CSC element 6 in order to carry out cell balancing of the cells measured by it, or to allow control to be applied to the pertinent semiconductor switches. Cell balancing is known from the existing art and is relevant in particular for the balancing of (different) states of charge (SOC) of individual cells 4 which are connected into an overall package.
The greater the number of cells connected together into a battery system, in particular the more CSC elements 6 that are coupled to one another using a single serial bus, the greater the load on communication bus 8a, due to the fact that individual CSC elements 6 generate their measured values mutually independently and then wish to transfer them via communication bus 8a. Depending on the degree to which such a system has been expanded, this can cause data bus 8a to be completely filled or in fact overloaded.